Dynamics and thermodynamics analysis of tropical cyclone ... · direction and vorticity of the flow. The concept of helicity was used in meteorology by Angell et al. (1968) for the

Journal of the Earth and Space Physics, Vol. 42, No. 4, Winter 2017, PP. 13-26

Dynamics and thermodynamics analysis of tropical cyclone Haiyan

Pegahfar, N.1* and Ghafarian, P.1

1. Assistant Professor, Atmospheric Sciences Research Center, Iranian National Institute for Oceanography and

Atmospheric Science, Tehran, Iran

(Received: 17 Oct 2015, Accepted: 18 Oct 2016)

Abstract

Tropical cyclone Haiyan (TCH) that formed over the West Pacific Ocean during 3-11

November 2013 has been investigated using three datasets of Japan Meteorology

Agency, ECMWF and NCEP. Strength of TCH has been studied using two synoptic

parameters of 10-m wind velocity and mean sea level pressure (MSLP). then, three

dynamic parameters including vertical wind shear (VWSH) vector, helicity and

potential vorticity (PV) together with the thermodynamic parameter of convective

available potential energy (CAPE) have been calculated and analyzed during TCH life

cycle. VWSH vector was analyzed in three classes of weak, moderate and strong shear,

having northeasterly direction for most of TCH lifetime. Moreover, the helicity

parameter was intensified to the tornadic instability (at about 6 hours later than the time

of maximum 10-m wind speed), and its anomaly was located in the downshear quadrants

for most of TCH life span. In addition, no significant PV anomaly was detected near

TCH, but a subtropical PV anomaly was extended to the Philippines Islands before TCH

eye reached this region. Also, CAPE parameter was intensified to strong instability class

at about 48 hours earlier than the time of maximum 10-m wind speed and its anomaly

was equally displaced in both up- and downshear quadrants. Finally, it can be concluded

that 30-hourly lag between the time of CAPE maximum value and VWSH for which

TCH was intensified to category 5.

Keywords: Tropical cyclone Haiyan, CAPE, Helicity, Potential vorticity, Vertical wind

shear vector.

1. Introduction

Some energetic atmospheric systems with

rotating motions have noticeable destructive

effects on human life and their financial

losses (Lee and Wurman, 2005). Meanwhile,

recognition of causes of formation,

intensification and weakening of tropical

cyclone (TC) is of importance, especially on

coastal regions. Hence, the relationship

between this phenomenon and climate

change has been intensively considered in

the last decade (e.g., Chan and Liu, 2004;

Chen, 2009; Emanuel, 2005; Webster et al.,

2005; Fan, 2007a; Fan, 2007b; Shepherd and

Knutson, 2007; Zhou et al., 2008). Also,

many research studies from different aspects

have been conducted to investigate TC using

numerical weather prediction (NWP) (e.g.

Ramalingeswara Rao et al., 2009), climate

models (Camargo and Sobel, 2004) and also

dense observational datasets. However, the

last item still provides the best multi-scale

analysis of TC. Some of variables and

applicable approaches highlighting the

importance of synoptic analysis in TC

investigation are presented below:

(I) a pre-existing disturbance with

sufficient amplitude in presence of air-sea

interaction, which is a favorable condition

for TC formation (Riehl, 1948; McBride and

Zehr, 1981; Gray, 1968),

(II) Planetary Boundary Layer (PBL)

parameters, affecting TC formation (Anthes

and Chang, 1978),

(III) minimum central surface pressure

related to SST between 26-30 oC (Titley and

Elsberry, 2000),

(IV) break down of the mentioned

relationship in item III for SST=30 oC

(DeMaria and Kaplan, 1994),

(V) intrusion of very moist near-

equatorial air into TC (Lajoie and Walsh,

2010),

(VI) angle of the equatorial air stream

inflow (Lajoie and Walsh, 2010), and

*Corresponding author: E-mail: [email protected]

14 Journal of the Earth and Space Physics, Vol. 42, No. 4, Winter 2017

(VII) vertical wind shear (Corbosiero

and Molinari, 2003; Chen et al., 2006). However, not only synoptic analysis of

routine parameters (Barry and Carleton,

2001) but also dynamics (Kurgansky, 2008)

and thermodynamic analysis (Molinari et al.,

2012) should be considered in growth and

development of a TC. Hence in the present

work, three dynamic parameters including

vertical wind shear (VWSH) vector, helicity

and potential vorticity (PV) together with

CAPE (Convective Available Potential

Energy) as a thermodynamic parameter

besides of some other routine synoptic

parameters have been investigated during

the life cycle of tropical cyclone Haiyan

(TCH). This study covers generation, mature

and dissipation processes of TCH. The rest

of this paper has been arranged to describe

theoretical basics (Sect. 2) and data and

methods (Sect. 3). Following, case study of

TCH is discussed in Sect. 4. Then, results

and discussion together with conclusions are

explained in Sect. 5 and 6, respectively.

2. Theoretical Framework

In this section, some characteristics of three

dynamics parameters including VWSH,

helicity and PV, together with

thermodynamic parameter of CAPE are

described, respectively.

(a) VWSH: this parameter, calculated

using ( 200 − 850), is known as a factor

with negative influence on TC intensity

change at all stages of its lifetime (Gray,

1968; DeMaria and Kaplan, 1994; Hanley et

al., 2001). Despite the uncertain nature of

this parameter, its role has been investigated

in (I) dry adiabatic dynamics (Raymond,

1992; Jones, 1995; Frank and Ritchie, 1999),

and (II) idealized numerical models of TCs

in creating azimuthal asymmetries of

convection (DeMaria, 1996; Frank and

Ritchie, 2001). Four general influences of

VWSH on asymmetric vertical motion

hypothesized by Jones (2000) have been

listed as below:

(1) Since VWSH is accompanied by

horizontal temperature gradient in balanced

flow, vortex flow along environmental

isentropes produces both downshear-upward

motion and upshear-downward motion

(Raymond, 1992; Jones, 1995).

(2) As VWSH begins to tilt the vortex, a

compensating secondary vertical circulation

is developed in an attempt to maintain the

balanced flow. This circulation, which

produces up- and downward motions in

down- and upshear parts in that order

(Raymond, 1992; Jones, 1995; DeMaria,

1996), acts to move the vortex back toward

a vertical orientation. In the adiabatic

framework, the secondary vertical

circulation also creates potential temperature

anomalies in the vortex, with a cold anomaly

in downshear part and a warm anomaly in

the upshear part of storm center.

(3) The isentropic flow along the vortex

is distorted by VWSH and results in the

upward motion to the right of the vertical tilt

vector, which is initially downshear

(Raymond, 1992). However, Jones (1995;

2000) demonstrated that vertical vortex

interactions rotate its tilt vector away from

downshear. Since upward motion is favored

right of the tilt vector and the favored

quadrant for upward motion also rotates with

time.

(4) The last mechanism is appeared by

the relative flow (the environmental flow

minus the motion of the vortex) along the

vortex isentropes associated with the warm

core (Corbosiero and Molinari, 2002). The

obtained pattern of this vertical motion

depends on the vertical profiles of wind and

potential vorticity in the vortex. This last

mechanism is secondary to the second and

third mechanisms discussed above.

(b) Helicity: Helicity is a standard factor

of rotation in every point of a flow

that corresponds to transfer of vorticity from

environment to an air parcel in a

convective motion. The concept of helicity,

proposed by Betchov (1961), is suitable for

prediction of extra-large cells with large and

relatively long lasting helicity. This

parameter is similar to curvature vorticity

and depends on the angle between the

direction and vorticity of the flow. The

concept of helicity was used in meteorology

by Angell et al. (1968) for the first time and

defined as:

H = ∫Vh . ζh dZ = ∫Vh

. ∇ × Vh dZ, (1)

Using the horizontal components of wind

velocity and vorticity ( Vh and ζh ,

respectively) and Z as the height. Focusing

on more than one fixed parameter is one of

http://en.wikipedia.org/wiki/Vorticity

http://en.wikipedia.org/wiki/Convection

Dynamics and thermodynamic analysis of tropical… 15

helicity advantage, compared with vorticity

parameter. The other main characteristic of

helicity is that it can be served to quantify

streamwise vorticity as a forecast tool for

super-cell and tornado environment (Jones

et al., 1990). Lilly (1986) pointed out that

larger values of helicity prevent energy of

flow from diffusing or scattering. Therefore,

this concept can be applied in the

investigation of intense convective storms

and tornados, in which strong vertical

motions exist and velocity and vorticity are

aligned in the same direction. A turbulent

fluid with large amount of helicity shows

reluctance for transfer of energy to inertial

range. Therefore, it can be inferred that

small-scale atmospheric fluid with large

amount of helicity is more stable and can be

predicted more easily, compared with those

with few amount of helicity.

According to some research studies,

strength of rotating phenomenon is related to

the helicity value (Davies, 2006; Weisman

and Rotunno, 2000) that is estimated at the

standard fixed layer of 0-1 or 0-3 km

(Rasmussen and Blanchard, 1998).

However, Thompson et al. (2007) showed

that estimation of helicity using inflow layer,

discriminates between significantly tornadic

and non-tornadic super-cell comparing with

standard fixed layer version of helicity.

Table 1 shows a list of categorized values of

helicity according to various instabilities.

It should be noted that TC itself provides

the environmental helicity for its individual

cells (Molinary and Vollaro, 2008). Also,

Khansalari et al. (2011) investigated the

applicability of helicity during cyclone

Gonu and showed that dynamic buoyancy

was the main factor in producing helicity.

(c) Potential Vorticity (PV): PV as a

quantity that is proportional to the dot

product of vorticity and stratification, is a

useful concept for understanding generation

of vorticity in cyclogenesis, analyzing

oceanic flows and tracing stratospheric air in

the troposphere. This concept was

formulized by Rossby (1940) and developed

by Ertel (1942) as:

𝑃𝑉 = 1

𝜌𝜁𝑎 . 𝛻𝜃, (2)

where θ is potential temperature, 𝜁𝑎

(containing Coriolis parameter of f = 2Ω sin

(φ)) is the absolute vorticity and 𝜌 is the fluid

density. To study PV generation due to latent

heat release and elimination of friction effect

on PV calculation, this parameter is

generally considered at 300 hPa and 700 hPa

pressure levels, respectively.

(d) Convective Available Potential

Energy (CAPE): CAPE is the amount of

energy that an air parcel should have to be

able to pass a special distance vertically in

the atmosphere. This parameter is actually

the positive buoyancy of an air parcel and

shows the sign of stability or instability

condition of the atmosphere. Hence, CAPE

plays a key role in numerical weather

predictions. The value of CAPE can be

calculated via the below equation

𝐶𝐴𝑃𝐸 = ∫ 𝑔 (𝑇𝑣, 𝑝𝑎𝑟𝑐𝑒𝑙−𝑇𝑣, 𝑒𝑛𝑣

𝑇𝑣, 𝑒𝑛𝑣) 𝑑𝑧.

𝑧𝐸𝐿

𝑧𝐿𝐹𝐶 (3)

Where zLFC is the free convection level

height, zEL is the balance level height

(neutral buoyancy), 𝑇𝑣, 𝑝𝑎𝑟𝑐𝑒𝑙 is the virtual

temperature of air, 𝑇𝑣, 𝑒𝑛𝑣 is the virtual

temperature of environment and g is the

gravitational acceleration. A list of stability

and instability stratifications corresponding

to CAPE values are shown in Table 2.

Table 1. Relationship between helicity and instability of the atmosphere (From http://www.theweatherprediction.com/habyhints/313/)

Instability Helicity (J/kg or m2/s2)

Supercells possible with weak tornadoes according to Fujita scale 150 < H < 299

Very favorable to supercells development and strong tornadoes 300 < H < 450

Violent tornadoes when calculated only below 1 km (4,000 feet), the cut-off value

is 100 450 < H

https://en.wikipedia.org/wiki/Vorticity

https://en.wikipedia.org/wiki/Stratification_(mathematics)

https://en.wikipedia.org/wiki/Cyclogenesis

http://en.wikipedia.org/wiki/Supercell

http://en.wikipedia.org/wiki/Tornadoes

http://en.wikipedia.org/wiki/Fujita_scale


Table 2. CAPE values correspond to various atmospheric instabilities (From http://www.tornadochaser.net/cape.html)

CAPE values (J/kg or m2/s2) Stability-instability

CAPE < 0 Stable

0 ≤ CAPE < 1000 Low instability

1000 ≤ CAPE < 2500 Moderate instability

2500 ≤ CAPE < 4000 Intensive instability

4000 ≤ CAPE Extreme instability

3. Data and methods

In the current paper, two sets of re-analysis

data have been used including (I) GFS-ANL

data with 0.5o × 0.5o spatial resolution at 26

vertical pressure levels, and (II) ECMWF-

ERA interim data with 0.75o × 0.75o

latitude–longitude horizontal resolution at

37 pressure levels, both with 6-hourly time

intervals. To focus on the selected area, data

have been analyzed over 100-160 oE and 0-

30 oN. Moreover, a dataset from local

stations produced by Japan Meteorological

Agency (JMA) have been used.

To calculate values of the considered

parameters in TCH eye, the values from the

nearest grid points to TCH eye have been

selected. Also at each time, data from a

square domain of 5o×5o centered by TCH

eye have been excluded to find the

maximum values of the considered

parameters. In addition, radial extend of up-

and downshear around a TC, introduced by

Corbosiero and Molinari (2002) (Figure 1),

has been used to address different direction

around TCH.

VWSH has been computed via (1) using

the formula of u200 − u 850, (2), applying the

method defined by Stevenson et al. (2014),

and (3) averaging values in a radius of 500

km, determined by a square of 5o × 5o

including 10 grid points in each direction,

respectively.

4. Case study: TCH

TCH was one of the strongest storms over

the West Pacific Ocean and affected the

south-east part of Asia, especially the

Philippines Islands. Figure 2a and b show

TCH track and the time evolution of its

intensity. This storm was generated from a

region of low pressure in the southeast of

Pohnpei in the Federated States of

Micronesia on the last hours of 2 November

2013 and reached the Philippines region

with the speed of 76.38 m/s on 7 November

2013. Based on the records, TCH was the

most lethal typhoon over the Philippines

Islands and developed to a super storm

thorough its westerly motion. It killed about

6300 people and caused 1785 missing and

2.86 billion USD of property damages. TCH

ultimately reached the northern part of

Vietnam on 10 November 2013 and

continued its activity until 12 November

2013, when entering the south-east coast of

Asia.

5. Results and discussion

Before presenting the dynamic analysis of

TCH, it is worthwhile to emphasize TCH

intensity using some routine synoptic

variables. Hence, the parameters of 10-m

wind velocity and mean sea level pressure

(MSLP) are analyzed in Sect. 5.1 and then

dynamics and thermodynamics analysis are

presented in Sect. 5.2.

Figure1. Radial extend of up- and downshear quadrants

around a TC, taken from Figure 3 in Corbosiero

and Molinari (2002). To show the wind shear

direction, results from Molinari and Vollaro

(2008) have been also added to the diagram.


Figure 2. (a) Track of TCH during 3-12 November 2013 and (b) the intensity of storm in 6-hourly intervals as colored

points, taken from (http://www.weather.gov.hk/wxinfo/currwx/tc_prevpos_1339.html)

5.1. Synoptic analysis

5.1.1. Wind velocity and pressure

Two variables of 10-m wind velocity and

MSLP have been studied from 3-11

November 2013 at TCH eye and eyewall.

Horizontal distributions of these two

variables are shown in Figure 3. Red circle

in all subplots shows TCH eye location.

TCH intensification can be deduced from the

comparison of the right and left columns in

Figure 3. Increase of anti-cyclonic curvature

of wind field (Figure 3a and b) and also the

horizontal gradient of MSLP (Figure 3c and

d) reveal that TCH peak activity occurred on

7 November 2013. Moreover, the westward

motion of TCH can be seen in Figure 3.

To elucidate the TCH intensity, Figure 4

was plotted using data measured at some

local stations. This Figure shows time series

of maximum wind speed in TCH eyewall

(Figure 4a) and the minimum pressure in

TCH eye (Figure 4b) during TCH lifetime,

both are based on Saffir–Simpson

classification. Figure 4 shows that TCH was

in category 5 for 2 days. Also, simultaneous

occurrence of maximum wind speed and

minimum pressure can be seen from this

figure with inverse behavior of

increasing/decreasing trends.

Figure 3. Horizontal patterns of 10-m wind velocity and pressure reduced to mean sea level at 0000 UTC 3 November

2013 (a and c) and 1200 UTC 7 November 2013 (b and d). The red circle in each subplot shows TCH eye

location.

http://www.weather.gov.hk/wxinfo/currwx/tc_prevpos_1339.htm


(a)

(b)

Figure 4. Time series of maximum 10-m wind speed (a) and minimum pressure (b), using JMA data. Colored layer in

(a) was depicted based on Saffir–Simpson categories denoted in the legend. Classification of TC intensity

for pressure is superimposed on each point in (b).

5.2. Dynamics and thermodynamics

analysis

5.2.1. VWSH vector

Time series of VWSH in TCH eye has been

calculated using the relation of 200 − 850

and plotted in Figure 5. According to

Corbosiero and Molinari (2002) findings,

three classes for VWSH including weak

(VWSH< 5 m/s), moderate (5 m/s < VWSH

< 10 m/s) and strong (VWSH > 10 m/s)

classes have been demonstrated in Figure 5

indicating the frequency of 5%, 17% and

78%, respectively. It is clear that the strong

class of VWSH around TCH eye location

reached maximum value of 45 m/s. Also, the

averaged values of VWSH in a square

domain of 5o × 5o around TCH eye

location have been calculated based on the

method defined by Stevenson et al. (2014)

for each time step. The results are shown as

the yellow bars in Figure 5. Frequency of the

averaged values of VWSH in weak,

moderate and strong classes, is 36%, 53%

and 11%, respectively.


Figure 5. Time variation of VWSH calculated in TCH eye location (cream bars) and the averaged values of VWSH

over a 5𝑜 × 5𝑜 square domain around TCH eye (yellow bars). Two horizontal dashed lines demonstrate

metrics defined by Corbosiero and Molinari (2002) as indicated in the legend.

The direction change of VWSH vector,

during TCH life cycle, is shown in Figure 6.

Analysis of VWSH vector magnitude

(Figure 6a) shows that shear value is

minimum at the beginning of TCH life (3

November 2013), then is maximized during

2 days (at the end of 5 November 2013),

afterward decreased until the end of 9

November 2013, and again is increased from

the beginning of 10 November 2013.

Increasing and decreasing trends of VWSH

is opposite to the TCH intensification trend.

Figure 6b shows the directional abundant

of VWSH vector and indicated that the most

of the shear vectors belong to the 180-240o

sector. Also, Figure 6b implies that the

direction of VWSH vectors do not always

aligned 180o opposite to the TCH motion

direction.

Moreover, the latitudinal - longitudinal

pattern of VWSH vectors for TCH is shown

in Figure 7. The rotational nature of VWSH

vector around TCH eye can be easily seen,

which is due to vortex interactions in the

vertical and leads to a rotation of tilt vector

away from downshear (Jones, 1995; 2000).

(a) (b)

Figure 6. Time series (a) and directional abundant (b) of VWSH vector during TCH life cycle.


Figure 7. Latitudinal - longitudinal distribution of VWSH vector at 0000 UTC 3 November 2013 (a) and 1800 UTC 7

November 2013 (b). The shaded patterns show the VWSH magnitude and the reference arrow of 10 m/s has

been show in the lower part of each subplot. The red circle shows TCH eye location in each subplot.

5.2.2. Helicity

Time series of helicity values in TCH eye

and eyewall is depicted in Figure 8. In this

figure, values of helicity in TCH eye could

not reached the possible supercell class,

except at 0000 UTC 6, 0600 UTC 7 and 10

November 2013 when the helicity exceeded

150 J/kg or m2/s2 value at the nearest grid

point to TCH eye. This can be referred to the

shrink of TCH eye so that the nearest grid

point could not be a representative of the

eye. This inaccuracy occurred due to the

poor horizontal resolution of the data.

Time variation of maximum values of

helicity, occurred out of TCH eye location,

and is depicted by solid thick line in Figure

8. It can be easily seen that at 0000 UTC 8

November 2013, helicity was maximized

(around 2000 J/kg value). Figure 8 also

shows that TCH was strengthened to the

tornadic supercell class and maintained in

this class for more than 102 hours, initiated

from 1200 UTC 5 November 2013 and

continued until the end of TCH lifecycle.

Gaining the great value of 2000 J/kg for

helicity clearly implies that TCH should

stand for a long time according to the results

reported by Droegemeier et al. (1993). They

showed that storms formed in environments

characterized by large helicity are longer-

lived than those in less helical surroundings.

To show the maintenance and propagational

characteristics of TCH based on helicity

parameter, as mentioned by Weisman and

Rotunno (2000) for other TCs, the horizontal

patterns of helicity are plotted for the whole

of TCH lifetime. The results are depicted for

3, 5, 7, 8 and 11 November 2013 in Figure

9. Helicity values of around 25 J/kg (at 0600

UTC 3 November 2013, Figure 9a) was

increased to a value of around 300 J/kg (at

1800 UTC 5 November 2013, Figure 9b). As

Figure 9c shows helicity was strengthened

and reached more than 550 J/kg value at

1800 UTC 7 November 2013. The

horizontal gradient of helicity reveals the

TCH intensity as well (Figure 9d). At the

end of TCH life span, the helicity value in

TCH environment was decreased to less than

300 J/kg, which was simultaneous with the

formation of a new helicity anomaly at the

southeast of TCH. The new helicity anomaly

was strengthened to 550 J/kg value and

reached near the TCH eye through 12 hours.

Results of applying the radial extend

standard, defined by Corbosiero and

Molinari (2002) (Figure 1) together with the

obtained VWSH vector direction for TCH

show that the first environmental helicity

anomaly was formed in the upshear part and

continued in downward half of TCH. Also

helicity anomalies was laid in the left

quadrants at the peak activity time of TCH

(7 and 8 November 2013). At 1800 UTC 9

November 2013, helicity anomaly was

entirely shifted to the downshear quadrants.

At the end of TCH life cycle, it slowly

moved to the right-downshear quadrant. It is

worthwhile to note that our findings are

similar to Molinari and Vollaro (2008)

results, as the maximum helicity value

occurred in the downshear-left quadrant for

Hurricane Bonnie (1998).


Figure 8. Time series of helicity (J/kg) in TCH eye (dotted line) and the maximum values occurred in its environment

(solid line). Colored layers show the relationship between the corresponding parameter and storm instability

classification, defined in the legend.

Figure 9. Horizontal patterns of helicity (J/kg) during TCH lifetime, at 0600 UTC 3 November (a), 1800 UTC 5

November (b), 1800 UTC 7 November (c), 0000 UTC 8 November (d), 0000 UTC 11 November (e) and

1200 UTC 11 November 2013 (f). Red circle in all panels demonstrates the eye location. Color bar has been

shown in the lower part of each subplot.


5.2.3. PV The horizontal patterns of PV were

calculated at two pressure levels of 300 and

700 hPa and are plotted for 7 and 9

November 2013 (Figure 10). Results

indicate that because of the TCH location in

the lower latitudes (near equator and with

near zero value of Coriolis parameter) no

significant PV was detected near TCH, at

neither 300 hPa nor 700 hPa. Only a

subtropical PV anomaly affected TCH

passing the equatorial latitude (< 8 oN) and

reaching subtropical region. On the 7 of

November 2013 and at 300 hPa level, a

subtropical PV anomaly with negative

values was extended to the Philippines

Islands before TCH eye reached this region

(Figure 10a), and it was diminished on 9

November 2013. At 700 hPa, a subtropical

negative PV anomaly can be seen over the

coast of Vietnam both on 7 and 9 of

November 2013.

5.2.4. CAPE

Time series of the thermodynamic parameter

CAPE (taken from GFS reanalysis data) is

plotted in TCH eye (Figure 11). Also

maximum values detected in the

environment of TCH was added to this

figure. Regarding the instability classes

defined for CAPE parameter, the values of

CAPE in the TCH environment belong to the

moderate and strong instability classes,

except for two values that occurred in the

last day that corresponded to the weak

instability class. The values of CAPE, at the

nearest grid point to TCH eye location, never

reached the strong instability classes, as a

calm weather expected for the eye. The

intrusion of CAPE values into the moderate

instability class, at the nearest grid point to

the TCH eye location, may be due to the

intensification of TCH and shrinking TCH

eye. So, the CAPE values may be used to

delete the eye location. Clarification for this

due to poor resolution of the reanalysis data,

that is not possible without numerical

simulations. Achieving the value of not

more than 3500 J/kg for CAPE shows that

TCH was not intensified to the extreme

instability class. Out of TCH eye location,

the maximum values of CAPE experienced

a frequency of 5% in a week, 61% in

moderate and 33% in strong instability

classifications.

Figure 10. Horizontal patterns of PV (PVU) during TCH life cycle at 1200 UTC 7 November 2013 (a and b) and at

0600 UTC 9 November 2013 (c and d). Left column depicts PV at 300 hPa and the right one shows that for

700 hPa. Red circle in each panel demonstrates TCH eye location.


Figure 11. Time series of CAPE parameter (J/kg) in TCH eye location (dotted line) and also the maximum values out

of TCH eye location (solid line). Colored layers show the corresponding instability classifications defined

in the legend.

Figure 12. Horizontal patterns of CAPE (J/kg) during TCH on 1800 UTC 5 November 2013 (a, b) and 1200 UTC 7

November 2013 (c, d). The right column has been prepared as the zoom of the left column. Red circle in all

panels demonstrates TCH eye location. Color bar has been shown in the lower part of each subplot.

The horizontal patterns of CAPE for

TCH is plotted for 5 and 7 November 2013

in Figure 12. A CAPE anomaly existed in

the northwest of TCH eye at the beginning

of its lifetime with a clear distance between

them until 5 November 2013. Two days

later, on 7 November 2013, TCH eye passed

the CAPE anomaly (values less than 1000

J/kg) and after 24 hours it was entirely

positioned in the west part of the CAPE

anomaly. Near zero values of CAPE on 8

and 10 November 2013 is remarkable. Such

low values refer to the stop time for vertical

motions and means that no feeding occurred

from the oceanic surface layer.

One of the other remarkable points is

equally positioning of CAPE anomaly in the

both upshear and downshear quadrants. Our

findings support the hypothesis argued by

Corbosiero and Molinari (2002) for

convectively active tropical cyclones, as a

deep divergent circulations oppose the

vertical wind shear and act to minimize the

tilt. This allows maximum convection to

remain without rotating with time. However,

Molinari and Vollaro (2010) indicated that


CAPE in strongly sheared storms was 60%

larger in downshear. Also Molinari and

Vollaro (2008) examined the spatial

variation of CAPE in Hurricane Bonnie

(1998) and concluded that the mean value of

CAPE was also 3 times larger in downshear.

6. Conclusion

In this research, the TCH as the strongest TC

formed over the West Pacific Ocean until

2014 was analyzed using some synoptic,

dynamics and thermodynamic parameters.

For this aim, three sets of JMA, ECMWF

and GFS-NCEP were used for the period of

3-12 November 2013. JMA dataset was

measured at some local stations while the

last two datasets are included in the

reanalysis data with the horizontal resolution

of 0.75𝑜 × 0.75𝑜 and 0.5𝑜 × 0.5𝑜,

respectively. For data processing, two parts

including eye and eyewall were defined for

TCH in 6-hourly time intervals. Also an

averaging method defined by Corboseiro et

al. (2002) was applied to determine the

VWSH vector at each time step.

Intensity of the selected TC, using the

synoptic parameters of 10-m wind velocity

and MSLP were analyzed that showed

intensification of TCH to category 5, based

on Saffir-Simpson scales. Simultaneous

occurrence of the maximum wind speed

(~value of 90 m/s) and the minimum surface

pressure (~ 895 hPa) were recorded at 1800

UTC 7 November 2013. Then the dynamics

parameters of VWSH, helicity and PV were

investigated. The obtained results are

itemized as below:

(1) TCH experienced all three classes of

weak, moderate and strong VWSH during its

life cycle. The maximum value of VWSH

occurred at 0000 UTC 7 November 2013.

Also VWSH vector, computed over a 5𝑜 × 5𝑜 square domain centered by TCH eye, had

the values of 36%, 53% and 11% for the

above three VWSH intensity classes,

respectively. Also, the dominant direction

for VWSH was northeasterly during TCH

period. The higher frequency of moderate

class of VWSH supports Nolan and

McGauley (2012) findings as the positive

role of VWSH in facilitating TC formation

and development.

(2) Helicity values during TCH reached a

value of 2000 J/kg and was laid in the

favorable supercell class. Also, the helicity

anomaly was located in the downshear

quadrants at most of the TCH lifetime.

According to the helicity time series, this

parameter was maximized at 0000 UTC 8

November 2013, at around 6 hours later than

TCH maximum activity time.

(3) No significant value of PV was seen;

neither at 300 hPa nor at 700 hPa. However,

a subtropical PV anomaly with negative

value (at 300 hPa level) extended to the

Philippines Islands before TCH eye reached

this area. So, it could be concluded that

accompanying the subtropical PV anomaly

together with TCH effects increased the

severe weather conditions over the

Philippines Islands.

Moreover, CAPE analysis showed that

this parameter was not strengthened to the

extreme instability class during TCH period

and only gained around 3500 J/kg value.

Also during TCH life cycle, the CAPE

anomaly was located at upshear and

downshear quadrants equally, while

Molinari and Vollaro (2008 and 2010)

introduced 60% larger values in downshear

part. As the other remarkable point, CAPE

was maximized at about 48 hours earlier

than TCH peak activity time. The observed

lag between the time of CAPE and helicity

maximum values (about 54 hours) can be

interpreted as this fact that updraft motion

should be intensified firstly and then rotation

could be strengthened. Therefore, it could be

acclaimed that this lag between the time of

CAPE and helicity maximum values is one

of the TCH characteristics. In spite of CAPE

cease for intensive instability class and not

reaching extreme instability class,

decreasing/increasing trend of

pressure/wind speed continued for 48 hours.

Finally, our findings showed that there

was an inconsistency between various

metrics of the TC classifications during TCH

life cycle. So 30-hourly lag between

occurrence of CAPE and VWSH maximum

values could be interpreted as one of the

probable reasons for TCH intensification to

category 5. Hence, it can be concluded that

the total synoptic, dynamics and

thermodynamic parameters together with

their dominance hierarchy influences on TC

should be focused on to access a vast feature

and description of a TC. Focusing on these

various parameters in terms of horizontal

distribution and time series allows the


evolution of TSs to be investigated using

meteorological tropical cyclone models.

Acknowledgements The authors are

thankful to the Iranian National Institute for

Oceanography and Atmospheric Science,

Tehran, Iran for their financial support for

this research (project No. 393-033-01) and

ECMWF and NCEP-GFS teams for

providing re-analysis data. The authors

would like to thank Dr. Maryam Gharaylou

for her insightful review.

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